Invitees have no time to speculate (5)
I believe the answer is:
guess
'to speculate' is the definition.
(I know that guess is a more specific form of the action speculate)
'invitees have no time' is the wordplay.
'invitees' becomes 'guests' ('guest' can be a synonym of 'invitee').
'have no' indicates named letters should be taken away.
'time' becomes 't' (abbreviation).
'guests' with 't' removed is 'GUESS'.
(Other definitions for guess that I've seen before include "Speculate" , "Hypothesis" , "Surmise" , "Imagine" , "Speculation" .)